Question: What is the greatest common factor of $28$ and $20$ ? Another way to say this is: $\operatorname{gcf}(28, 20) = {?}$
Solution: The greatest common factor is the largest number that is a factor of both $28$ and $20$ The factors of $28$ are $1$ $2$ $4$ $7$ $14$ , and $28$ The factors of $20$ are $1$ $2$ $4$ $5$ $10$ , and $20$ Thus, the greatest common factor of $28$ and $20$ is $4$. $\operatorname{gcf}(28, 20) = 4$